This application is a revised proposal to assess aspects of adrenergic receptor and P2Y purinergic receptor signalling. Our recent, preliminary data for this application include the identification and cloning of five different P2Y receptors in MDCK-D1 cells and discovery of a key role of ATP release as an autocrine/paracrine mechanism for establishing basal levels of signal transduction in these cells. The proposed studies will focus on studies in MDCK-D1 cells, designed to define information regarding nucleotide release and autocrine/paracrine signalling by P2Y-receptors, stoichiometry and compartmentation of G protein-coupled receptors/G protein and effector molecules, agonist-promoted regulation of adrenergic and P2[unreadable]-receptors, and in parallel studies using murine knockouts, the role of P2Y receptors and adrenergic receptors in regulation of renal function. The studies will test several hypotheses, including the possibilities that: 1) nucleotide release is a critical factor for the set point of multiple signal transduction pathways; 2) P2Y receptors, A1-AR and (B2-AR differentially target in polarized MDCK cells, and create compartmentalized signalling microdomains; and 3) adrenergic and P2Y receptors will show evidence of"cross regulation." The latter may contribute to modulation of response via sympathetic postganglionic neurons in the kidney and other cells. In additional experiments, we will attempt to define the functional activity of adrenergic and P2[unreadable] receptors in vivo by the studies of mice with knockouts of certain receptors. Overall, the data should provide new insights into regulation of epithelial cells, in particular renal epithelial cells, by adrenergic and P2Y receptors and should help define the cell and renal physiological role of those receptors. In addition, the findings may have pathophysiologic and therapeutic implications for diseases such as cardiovascular, renal, and other disorders that involve the sympathetic nervous system or in which cell injury leads to release of nucleotides.